c - 尝试将 'insert' 或 'add' 写入文本文件 - 一个小问题

Question

提供代码 M.R.E。

症状是“简单”:

1. 尝试 hello\nhello\nhelloEOF 并插入 '_' @ ln=2 & col=1 (或者更确切地说是任何 line>1 && col==1)程序奇怪地做对了，但是吃掉了 '\n' ，导致第 2 行与第 1 行 融合 - hello_hello\nhelloEOF，而不是 hello\n_hello\nhelloEOF。
2. 尝试在文件 hello\nhello\nhelloEOF 的最后一行中插入 '_' @ ln=3 & col=5(或者更确切地说，在由 EOF 终止的行中的任何字符 col>1)导致它跳过最后一个实际字符行:hello\nhello\nhell_EOF 而不是 hello\nhello\nhell_oEOF。
3. 尝试使用最后一行中的第一个字符(col==1 in line terminated by EOF)导致错误消息(\n Invalid Index.)扔了。

就我的直觉而言，我认为在处理行终止 ('\n',EOF) 及其计算方式时存在缺陷通常作为循环计数器，但我不明白。

想法/算法:

• 从用户处获取源文件
• 获取用户索引(行、列)
• 从源代码复制到 tmp 文件，直到(用户索引 -1 col)。
• 现在，允许用户将字符串写入 tmp 文件的缓冲区。
• 一旦用户终止输入，从用户索引复制到 tmp 直到 EOF。
• 重命名/删除+重命名 tmp 作为用户源文件的名称。

下面的代码完成了所有真正的对话:

#include <stdio.h>
#include <string.h>

/* Likely error region in chknmove(), chkncpy() and/or main() ;
   All other functions used are also provided */

long long lncnt(FILE *lcount){
/* counts the number of lines in a file with fgets() */
    rewind(lcount); /* ensures lines counted from beginning */
    long long lines=0; char line[501];
    while((fgets(line,501,lcount))!=NULL){
        lines++;
    }
    rewind(lcount); /* leaves fptr @ 0,0 rather than EOF */ 
    return lines; 
}
int chknmove(FILE *tomove, long long line, long long col){
/* Function to check & move FILE* to certain line/col */
    rewind(tomove); /* make sure fptr is at beginning of file */
    int f=0; /* set check-variable to 0 for successful */
    if(line<1 || col<1)
        f = -1; /* Ln,col cannot be -ve or even 0 -> 1st col is @ 1ln,1col in any non-empty file */
    else{
        long long i,q; i=1;q=0; /* i = lines seen, q = cols seen */
        /* i init to 1 for ease of comprehension v/s testing 'line-1' */
        while(i<line || q<col){ /* loop must iterate until i==line && q==col */
            int ch = fgetc(tomove); /* int to store EOF */
            if(ch==EOF){
                f=-1; break; /* if file ends before reaching index, failed. */
            }
            else if(ch=='\n') {
                if(i==line){
                    f=-1; break;/* if line ends before reaching col in ln, failed. */
                }
                i++; q=0; /* else , increase i by 1 and set q (col) to 0 */
            }
            else
                q++; /* any other character is 'normal' , just increment q (col) by 1 */
        }
    }
    if(f==0){ 
        fseek(tomove,-1,SEEK_CUR); 
        /* since index must be checked, loop reaches it -> fseek(-1) causes *next* r/w to fptr to be on the index . */
        return 0;
    }
    else{
        /* f != 0 : moving has failed. */
        printf("\n Invalid Index.\n");
        return -1;
    }
}
int chkncpy(FILE *source, FILE *dest,long long beginln, long long begincol, long long endln, long long endcol){
    rewind(source); int f=0;
    if(beginln<1 || begincol<1 || endln<beginln || endcol<1 || (beginln==endln && endcol<begincol))
        f=-1; /* line/col must be >= 1 in non-empty file, copying done top to bottom (begin-index <= end-index ) */
    else{
        if(chknmove(source,beginln,begincol)==0){
        /* loop begins if begin-index is valid */
            long long i,q; i=beginln;q=begincol; /* i = lines, q = cols */
            while(i<endln || q<endcol){
                /* while end-index is not reached : !(i==endln && q==endcol) */
                int ch = fgetc(source);
                if(ch==EOF) {f=-1; break;} /* File ends b/w begin-index & end-index - failed. */
                else if(ch=='\n') {
                    if(i==endln) {f=-1; break;} /* endln ends before reaching endcol - failed */
                    i++; q=0;
                    fputc(ch,dest); /* valid '\n' put in dest file */
                }
                else{
                    q++; fputc(ch,dest); /* valid char put in dest file */
                }
            }
        }
        else f=-1; /* if begin-index is invalid, failed. */
    }
    if(f==-1){
        /* if f != 0 : chkncpy() failed */
        printf("\n Invalid Index.\n");
        return -1;
    }
    else /* if f remains == 0 */ return 0;
}
long long lastlncol(FILE *fyl){
    rewind(fyl); /* makes sure fptr @ beginning */
    chknmove(fyl,lncnt(fyl),1); /* move to last line */
    long long cnt=0; /* cnt stores no. of chars in last line */
    while(1){
        int g = fgetc(fyl);
        if (g==EOF)
            break; /* EOF not counted */
        else if(g=='\n'){
                cnt++;break; /* \n is counted as a char, but also as EOL */
            }
        else
            cnt++; /* all other chars counted */
    }
    rewind(fyl); /* leaves file at its beginning */
    return cnt;
}
long long lcc(FILE *fyl,long long line){
    rewind(fyl); int f = chknmove(fyl,line,1); /* moves fptr to line */
    long long cnt=0;
    if(f==0){
        while(1){
            int g = fgetc(fyl);
            if (g==EOF)
                break;
            else if(g=='\n'){
                cnt++;break;
            }
            else
                cnt++;
        }
        rewind(fyl);
        return cnt;
    }
    else
        return -1;    
}
void writer(FILE *write, int ctrl){
    printf("\n Terminate Input with \"/end/\".\n\n   Type below :\n\n");
    char in[501]; /* str that stores input line-by-line */
    char *p; int o;
    while(1){
        fgets(in,501,stdin); /* takes line from user */
        if((p=strstr(in,"/end/"))!=0){ 
            /* if line has "/end/", all chars till /end/ are written to file and input loop breaks */
            o = p-in;
            fprintf(write,"%.*s",o,in);
            break;
        }
        else{
            /* writes line to file */
            fputs(in,write);
        }
    }
    if(ctrl==0){
        /* in some cases, file must not be closed yet , hence ctrl is taken */
        int s = fclose(write);
        if(s==EOF) printf("\n Error ");
        else printf("\n Success.\n");
    }
}
void eat() /* clears stdin */
{
    int eat;while ((eat = getchar()) != '\n' && eat != EOF);
}

int main(){
    /* main to add/insert to file @ given index */
    char fadd[501];/* filename str */ 
    printf("\n Filename : "); scanf("%500[^\n]",fadd);
    FILE * add = fopen(fadd,"r");
    if(add==NULL)
        perror("\n Error "); /* if file does not pre-exist */
    else{
        long long line, col; char sep; printf("\n Index : "); scanf("%lld%c%lld",&line,&sep,&col); /* takes index in ln-char-col form */
        eat(); /* clears stdin */
        FILE * tmp=fopen("Temp.Ctt","w"); /* opens a tmp file to write */
        if(tmp==NULL)
            perror("\n Error "); /* failed - tmp file could not be created to write */
        else{
            int f; /* success var */
            if(line==1 && col>1){
                /* if user wants to insert @ a col>1 in line 1 */
                f = chkncpy(add,tmp,1,1,line,col); /* all below calls intend to write till 1 char before the char @ given index */
            }
            else if(line>1 && col>1){
                /* if user wants to insert @ a col>1 in any line>1*/
                f = chkncpy(add,tmp,1,1,line,col-1);
            }
            else if(line>1 && col==1){ //ERRORS - ignores the '\n' of line-1
                /* if user wants to insert @ a 1st col in line>1 */
                f = chkncpy(add,tmp,1,1,line-1,lcc(add,line-1));
            }
            else if(line==1 && col==1){
               /* if user wants to insert @ 1,1 (no moving/copying needed) */
                f=0;
            }
            else{
                printf("\n Invalid Index.\n");f=-1;
            }
            if(f==0){
                writer(tmp,1); 
                /* calls function to allow user to write to fptr , with ctrl != 0, so writer() *won't* fclose(tmp) */
                chkncpy(add,tmp,line,col,lncnt(add),lastlncol(add));
                /* copies all characters from index till EOF */
                int ok = fclose(tmp); fclose(add);
                if(ok==EOF){
                    /* if closing tmp was unsuccessful, the file on disk may be corrupted/incomplete, so must be removed */ 
                    remove("Temp.Ctt");perror("\n Error ");

                }
                else{
                    if(rename("Temp.Ctt",fadd)==0)
                        printf("\n Success.\n");
                    else{
                        /* on Windows & some other non-POSIX systems, file cannot be renamed to pre-existing filename , hence delete original */
                        remove(fadd);
                        if(rename("Temp.Ctt",fadd)==0)
                            printf("\n Success.\n");
                        else{
                            /* if rename still unsuccessful, throw an error, remove tmp file and give up */
                            remove("Temp.Ctt");
                            perror("\n Error ");
                        }  
                    }
                }

            }
        }
    }
}

如果有任何遗漏的细节或无意的错误，请发表评论，我会更正它们。

Answer 1

你的代码太复杂了:

• 复制文件开头的不同情况应该合并到一个函数调用中，该函数调用将数据复制到并排除 col 行 line< 上的字节.

• 然后您从用户输入中复制。

• 最后复制输入文件的其余部分。

• 代码假定行和列从 1 开始编号。这可能是显而易见的，但您应该具体说明这一点，因为它可能对每个人来说都不是显而易见的。

• 这种风格很难阅读:你应该在二元运算符周围使用水平空间，在关键字、、 和 ; 之后和 {< 之前。在一行中塞满多个语句也不是一个好主意。

这是一个简化版本。通常，大部分代码用于错误处理:

#include <stdio.h>
#include <string.h>

void flush_line(FILE *fp) { /* read the rest of the current line */
    int c;
    while ((c = getc(fp)) != '\n' && c != EOF)
        continue;
}

int copy_file(FILE *from, FILE *to) {
    int c;
    while ((c = getc(from)) != EOF) {
        if (putc(c, to) == EOF)
            return EOF;
    }
    return 0;
}

int copy_lines(FILE *from, int line1, int col1, FILE *to) {
    int c, line = 1, col = 1;
    for (;;) {
        if (line >= line1 || (line == line1 && col >= col1))
            break;
        if ((c = getc(from)) == EOF)
            break;
        if (putc(c, to) == EOF)
            return EOF;
        col++;
        if (c == '\n') {
            line++;
            col = 1;
        }
    }
    return 0;
}

int writer(FILE *write) {
    char in[501]; /* str that stores input line-by-line */
    char *p;

    printf("\n Terminate Input with \"/end/\".\n\n   Type below :\n\n");
    while (fgets(in, 501, stdin)) {
        if ((p = strstr(in, "/end/")) != NULL) {
            /* if line has "/end/", all chars till /end/ are written to file and input loop breaks */
            int o = p - in;
            if (fprintf(write, "%.*s", o, in) < 0)
                return EOF;
            break;
        } else {
            /* writes line to file */
            if (fputs(in, write) < 0)
                return EOF;
        }
    }
    return 0;
}

int main() {
    /* main to add/insert to file @ given index */
    const char *temp_filename = "Temp.Ctt";
    char fadd[501];/* filename str */

    printf("\n Filename : ");
    if (scanf("%500[^\n]", fadd) != 1)
        return 1;
    flush_line(stdin);

    FILE *add = fopen(fadd, "r");
    if (add == NULL) {
        perror("\n Cannot open input file");
        return 1;
    }
    int line, col;
    /* read the index: 1 based line and column numbers */
    printf("\n Index : ");
    if (scanf("%d%*c%d", &line, &col) != 2) {
        fprintf(stderr, "invalid input\n");
        return 1;
    }
    flush_line(stdin);
    FILE *tmp = fopen(temp_filename, "w");
    if (tmp == NULL) {
        perror("\n Cannot create temporary file");
        fclose(add);
        return 1;
    }
    if (copy_lines(add, line, col, tmp)) {
        perror("\n Error copying beginning of file");
        fclose(add);
        fclose(tmp);
        remove(temp_filename);
        return 1;
    }
    if (writer(tmp)) {
        perror("\n Error writing user input");
        fclose(add);
        fclose(tmp);
        remove(temp_filename);
        return 1;
    }
    if (copy_file(add, tmp)) {
        perror("\n Error copying remaining file contents");
        fclose(add);
        fclose(tmp);
        remove(temp_filename);
        return 1;
    }
    fclose(add);
    if (fclose(tmp) < 0) {
        /* if closing tmp was unsuccessful, the file on disk may be corrupted/incomplete, so must be removed */
        perror("\n Error closing temporary file");
        remove(temp_filename);
        return 1;
    }
    if (rename(temp_filename, fadd) == 0) {
        printf("\n Success.\n");
        return 0;
    }
    /* on Windows & some other non-POSIX systems, file cannot be renamed to pre-existing filename , hence delete original */
    if (remove(fadd)) {
        perror("\n Cannot remove input file");
        remove(temp_filename);
        return 1;
    }        
    if (rename(temp_filename, fadd) == 0) {
        printf("\n Success.\n");
        return 1;
    }
    /* if rename still unsuccessful, try and copy contents */
    tmp = fopen(temp_filename, "r");
    if (tmp == NULL) {
        perror("\n Cannot re-open temporary file, output is in Temp.Ctt");
        return 1;
    }
    add = fopen(fadd, "w");
    if (add == NULL) {
        perror("\n Cannot re-open input file, output is in Temp.Ctt");
        fclose(tmp);
        return 1;
    }
    if (copy_file(tmp, add)) {
        perror("\n Error copying temporary file to input file");
        fclose(add);
        fclose(tmp);
        return 1;
    }
    fclose(tmp);
    if (fclose(add) < 0) {
        perror("\n Error closing input file");
        return 1;
    }
    /* throw an error, remove tmp file and give up */
    remove(temp_filename);
    printf("\n Success.\n");
    return 0;
}